The Federal Railroad Administration (FRA) reported, as of Dec. 1, 2006, that between 1995 and 2005 a total of 276 derailments occurred on the four Class I U.S. railroads and that these derailments were caused by broken rails. One of these derailments occurred on Mar. 17, 2001 and involved the Amtrak California Zephyr bound from Chicago to Oakland, Calif. This derailment caused one fatality, 77 injuries and $338 million dollars in property damage. The cause was a broken rail later found to have multiple internal defects due to metal fatigue.
A study of service failures on Class I railroads by the Transportation Technology Center, Inc. (TTCI) indicates that certain internal rail defects may be undetectable with current ultrasonic technology. In particular, one of the more problematic defects to locate with existing technology are detail fractures that are caused by metal fatigue and are masked by rail surface and subsurface shelling conditions, rail head profile (i.e. heavily worn rail), orientation of the defect and transducer-to-rail coupling. The need exists to develop a detection technique that is capable of locating internal defects in railroad rails due to metal fatigue that have heretofore been difficult or impossible to detect.
It is an object of the present invention to provide more effective and complementary non-destructive testing (NDT) technologies to reliably detect internal rail defects even with rail surface damage, heavily worn railroad profiles and different transducer orientations.
U.S. Pat. Nos. 4,165,648 and 4,174,636, both of which are incorporated herein by reference, describe one prior art method for detecting fractures in a railroad rail. More particularly, these two patents describe a system and method for performing ultrasonic inspection of a length of test material, such as a rail, with an ultrasonic transducing system emitting a beam of ultrasonic energy from within a pair of leading and trailing sealed wheels transparent to the ultrasonic beam and arranged for rolling contact along the test material.
In each of the leading and trailing wheels, ultrasonic transducers are oriented so that a beam of ultrasonic energy emitted from a transducer in one wheel will enter the test material, be reflected from the bottom surface thereof, and be directed to and received by a transducer in the same wheel or the other wheel. A reading of the transmitted energy indicates whether energy has been deflected away from the receiving transducer by defects in the test material. The transducers in each wheel are arranged to alternately transmit and receive.
The leading and trailing wheels are also provided with a longitudinally-looking transducer for emitting a beam of ultrasonic energy into the test material in advance of and behind the moving wheel means, e.g., at an angle of about 70° perpendicular to the test material surface. Additional zero degree transducers in each wheel can also emit radiation perpendicular to the test material.
Although the teachings in these two prior art patents did improve upon the detection of fractures in a railroad rail certain detail fracture types remain difficult to detect. It is therefore an object of the present invention to provide a system and method for detecting detailed fractures in a test material, such as a railroad rail, that were heretofore difficult if not impossible to detect with known prior art technology.
Due to the high cost of railroad derailments, both in terms of property damage and human injury or death, various scientific and technical bodies have investigated the cause of internal rail defects to determine the specific characteristics of such defects that could be used to improve detection. Although various characteristics have been found which lead to rail failure those characteristics have not been detectable on a commercial scale as they are below the detectable threshold of ultrasonic technology currently used in the detection industry.
It is therefore another object of the present invention to provide a commercially viable detection system able to detect the heretofore undetectable characteristics of a railroad rail which can lead to rail failure.